1. Field of the Invention
The present invention relates to an axle driving apparatus including a hydrostatic transmission (HST), an axle, and a transmitting mechanism for transmitting power from the HST to the axle, all of which are integrally provided in a housing of the axle driving apparatus. More particularly, two oil sumps separated by a partition are disposed in a housing. The HST is disposed in one of the oil sumps and the axle and so on are disposed in the other oil sump. When the volume of the oil sump fluctuates due to changes of the HST, oil is given to and received from the other oil sump, Therefore, the oil sump that houses the HST is supplied with oil with stability without a reservoir tank.
2. Related Art
There has been a well-known conventional axle driving apparatus including an HST hydraulically interconnecting a pump and a motor. Axles and a transmitting mechanism (including a differential gear) connect the HST to the axles together housed in a housing, wherein, as disclosed in JP Laid Open No. H3-159822, for example, two oil sumps have been formed in the housing so that the HST has been immersed in one of the oil sumps and the axles and the transmitting mechanism have been immersed in the other oil sump. In this regard, the volume of oil in the housing necessarily changes according to driving of the HST or change of oil temperature, thereby requiring an oil reservoir tank to accommodate the increased oil in the housing, which has been usually disposed above the housing.
Because of the reservoir tank projecting upwardly from the housing, the conventional apparatus has required large vertical space for its installation onto a vehicle, thereby making the vehicle rather tall. When the vehicle is designed like this, it becomes somewhat difficult for an operator to get on and off the vehicle, or its center of gravity is positioned unstably high.
For example, a lawn tractor having a mower disposed on the lower portion of a chassis between a front and a rear wheel and a grassbox disposed on the rear portion of the vehicle is well-known. On this tractor, a duct is disposed for sending grass rearwardly into the grassbox for collecting therein. Then, when a conventional axle driving apparatus, described above, is mounted onto the axle of the rear wheels of the lawn tractor, it is necessary to place the axle driving apparatus on the upper portion of the tractor and to extend the duct under the axle driving apparatus. In sum, there has been the problems that the reservoir tank, which is mounted on the top of housing of the axle driving apparatus, interferes with the chassis, and the arrangement and size of the duct is restricted.
Accordingly, it is a primary object of the present invention is to provide an axle driving apparatus, comprising an HST; an axle having a lateral axis of rotation; and a transmitting mechanism for transmitting power from a hydraulic motor of the HST to the axle, housed together in a housing forming an oil sump therein wherein the oil sump, in which the HST is disposed, is supplied with oil with stability by a compact oil-supplying construction without a reservoir tank.
To attain the primary object, the housing includes a first oil sump and a second oil sump. The HST is disposed in the first oil sump. The axle and the transmitting mechanism are disposed in the second oil sump and a communication means is disposed between the first oil sump and the second oil sump. The communication means makes oil flow therethrough from the first oil sump to the second oil sump when oil in the first oil sump is expanded beyond the volume of said first oil sump.
In a first construction, the first oil sump is separated from the outside air, the second oil sump is communicated with the outside air, a first open end of the communication means communicates with the first oil sump and is disposed above the oil level of the second oil sump. A second open end of the communication means communicates with the second oil sump and is disposed below the oil level of the second oil sump.
In the first construction, a partition is formed in the housing for separating the first oil sump and the second oil sump from each other. A third oil sump constitutes a part of the communication means and is formed in the housing above the partition. A conduit constitutes a part of the communication means and extends in the oil second sump from the third oil sump, so that a lower end of the conduit is defined as the second opening end of the communication means.
Alternatively, in the first construction, a partition is formed in the housing for separating the first oil sump and the second oil sump from each other. An oil passage is bored through the partition for constituting the communication means. The oil passage has vertical difference between its both open ends, so that an upper open end of the oil passage is defined as the first opening end of the communication means and a lower open end of the oil passage is defined as the second opening end of the communication means.
In a second construction, the first oil sump is separated from the outside air, and the second oil sump is communicated with the outside air. A partition is formed in the housing for separating the first oil sump and the second oil sump from each other, A first check valve is disposed at an opening end of the communication means communicating with the first oil sump for enabling oil to flow only from the first oil sump to the second oil sump. A second check valve is disposed between the first oil sump and second oil sump through the partition for enabling oil to flow only from the second oil sump to the first oil sump. The second check valve is disposed below the oil level in the second oil sump.
In a third construction, a partition is formed in the housing for separating the first oil sump and the second oil sump from each other. A clearance, formed in the housing above the partition, constitutes the communication means so as to make the first oil sump and the second oil sump communicating with each other therethrough. A check valve is disposed through the partition between the first oil sump and the second oil sump. The check valve enables oil to flow only from the second oil sump to the first oil sump, and the check valve is placed below the oil level in the second oil sump.